Ball bearings typically use a ball separator or cage to space the balls in the annulus between the inner and outer races, which are part of the inner and outer rings. FIG. 1A is a plan view and FIG. 1B is a cross-sectional view through a typical prior art bearing 20 having inner ring 22 with inner race 23, outer ring 24 with outer race 25, balls 26 and ball cage 28. FIG. 2 is a perspective view of ball cage 28 of bearing 20 with rings 22, 24 and balls 26 omitted. The cage is positioned through contacts with the balls and either the inner or outer race. The cage keeps the balls approximately evenly spaced around the bearing and reduces friction and wear by preventing contact between adjacent balls. However, the cage is an additional dynamic element in the system. It is free to move in all degrees of freedom, that is, rotationally, torsionally and translationally, within limits constrained by ball and race contacts. Because of this freedom of motion, the cage can experience unwanted oscillations known as instabilities. These instabilities can occur as linear oscillations, as torsional oscillations and/or elliptical oscillations known as whirl modes. When a cage becomes unstable it dissipates energy which increases the drag torque of the bearing, increases cage wear at the contact points and increases bearing operating temperatures, all of which can have a negative impact on bearing life. Bearing vibrations can also be transmitted to the equipment being supported by the bearing and the base supporting the bearing, thereby having a negative impact on the overall system performance.
Several approaches have been used to minimize cage or other bearing instabilities. For example, judicious selection of race and ball pocket clearances and proper lubrication can reduce some cage instabilities. Improvement can also be had by using more complex bearing structures such as are described, for example, in U.S. Pat. No. 3,918,778 to Jacobson et al, and U.S. Pat. No. 6,196,721 B1 to Farkaly. Other approaches external to the bearings have also been used to reduce overall vibrations such as for example are described in U.S. Pat. No. 6,682,219 B2 to Alam et al; U.S. Pat. No. 5,247,855 to Alten et al; U.S. Pat. No. 6,358,153 B1 to Carlson et al; U.S. Pat. No. 6,422,083 B1 to Hobbs; U.S. Pat. No. 6,641,119 B2 to Kato; U.S. Pat. No. 5,816,373 to Osterberg et al; U.S. Pat. No. 5,873,438 to Osterberg et al; and U.S. Pat. No. 5,522,815 to Schierling et al. Nevertheless, such approaches are only partially successful in controlling bearing cage instabilities and can be unduly complex and more expensive than is desired. Thus, there continues to be a need for effectively and inexpensively reducing cage instabilities in bearings
Accordingly, it is desirable to provide an improved bearing cage structure that can damp unwanted cage oscillations. In addition, it is desirable that the improved cage structure be simple, rugged and reliable and involve minimal modification of the overall bearing structure and size. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.